1. Field of the Invention
This invention relates to electrical switching apparatus, especially such apparatus as circuit breakers, network protectors and switches used in electric power circuits carrying large currents. More particularly, it relates to such apparatus with restriction of access to the push buttons used to operate the apparatus.
2. Background Information
Electrical switching apparatus for opening and closing electric power distribution circuits typically utilize an energy storage device in the form of one or more large springs to close the contacts of the device into the large currents which can be drawn in such circuits. Such electrical apparatus includes, for instance, power circuit breakers and network protectors which provide protection, and electrical switches which are used to energize and deenergize parts of the power circuit or to transfer between alternative power sources. These devices also include an opening spring or springs which rapidly separate the contacts to interrupt current flowing in the power circuit.
The operating mechanisms of these electric power switching devices include close and open push buttons which may be operated to release springs to close and open the contacts of the switch respectively. Typically, these push buttons are mounted side-by-side on the front of the apparatus. When the switching apparatus is used as a transfer switch to provide connections to alternate sources of power for an electric power distribution system, it is known to mount the switches side-by-side with a mechanical interlock which prevents having both switches closed at the same time. U.S. patent application Ser. No. 08/998,873, filed on Dec. 29, 1997, discloses such an interlock in which a slide bar mechanically blocks actuation of the close push button on one switch when the other is closed.
There are other situations where it is desirable to prevent unauthorized actuation of the push buttons of electrical switching apparatus. For instance, in some situations it is desirable not to close the switch until certain conditions have been satisfied, such as for example, that the load is turned off. Other examples include critical equipment which should not be turned off, hence access to the open push button should be controlled. In some installations the apparatus is controlled remotely through solenoids rather than the push buttons and it is desired therefore that the push buttons not be actuated. In other circumstances, the restriction of access may be just to prevent accidental actuation of the push buttons, but not to deny access. In all of these cases there can be circumstances where the push buttons should be operable despite the restricted access.
There is a need, therefore, for improved electrical switching apparatus in which access to the push buttons is restricted.
There is also a need for such apparatus in which the restriction access to the push buttons is selective.
There is a further need in some applications for the capability of overriding the restriction of access to the push buttons.
There is an additional need for such access restricting apparatus which is easily and economically manufactured and installed and retrofitted to existing equipment.